The present invention relates to controlled atmosphere rooms and more particularly to pressure/vacuum relief systems for controlled atmosphere rooms.
Controlled atmosphere rooms are commonly used for the storage of fruits, vegetables and other perishable commodities. Through proper control of atmosphere, including gas mixture, humidity and temperature, the ripening of commodities within the controlled atmosphere room can to a large extent be controlled. A typical controlled atmosphere room includes an enclosure capable of receiving a store of fruits, vegetables or other perishable commodities, as well as gas and temperature control systems that are capable of monitoring and maintaining the desired gas mixture and internal room temperature. Various factors, such as temperature changes, commodity respiration, commodity transpiration and the introduction and exhaust of gases, can have a significant impact on pressure within the controlled atmosphere room. If not properly controlled, these changes in pressure can cause damage, for example, to the walls or ceiling of the controlled atmosphere room.
In a typical application, one or more controlled atmosphere rooms are situated within a larger building. For example, a conventional application having six controlled atmosphere rooms 100 is shown in FIGS. 1-4. Each controlled atmosphere room 100 includes a storage enclosure that is isolated from the exterior 102 and includes an atmosphere control system that maintains the desired temperature, humidity and gas mixture (See FIGS. 1 and 3). Typically, the control system is automated, relying on sensors that provide measured atmospheric conditions to a controller. The controller analyzes the measured conditions and takes the appropriate action to maintain the interior of the controlled atmosphere within the desire parameters. Proper atmospheric pressure is typically maintained using a passive arrangement of valves that allow the room to vent gas when overpressure and to draw gas in from the environment when under pressure. In this context, the term “passive” in used to indicate that the valves are directly actuated by air pressure and are not computer controlled or otherwise automated. The primary functional component in a conventional pressure/vacuum relief system is a pressure relief valve 104 that includes separate vacuum and pressure valves. In use, when a sufficient negative pressure differential builds between the controlled atmosphere room 100 and the vacuum valve inlet 106, the vacuum valve opens, thereby allowing air from outside the controlled atmosphere room 100 to be drawn in through the pressure relief valve through the vacuum valve inlet 106. As the pressure equalizes, the vacuum valve automatically closes to again isolate the controlled atmosphere room 100. Similarly, when a sufficient positive pressure differential builds between the controlled atmosphere room 100 and the pressure valve outlet 108, the pressure valve opens, thereby allowing air from inside the controlled atmosphere room 100 to vent through the pressure relief valve 104. As the pressure equalizes, the pressure valve closes to return the controlled atmosphere room to isolation.
With a conventional system, the relief valve 100 is disposed outside the controlled atmosphere room 102. To prevent the relief valve 100 from being subjected to external weather conditions, such as snow, rain, or freezing temperatures, the pressure relief valve 100 is typically situated outside the controlled atmosphere room 100, but inside the larger building 110. For example, the relief valve 104 may be situated in an overhead space 114, such as shown in FIGS. 1, 3 and 4. It is generally undesirable to exhaust gases from inside the controlled atmosphere room 100 into the larger building 110, where the gases might have a negative impact. As a result, the pressure relief valve 104 typically includes an exhaust pipe that runs from the relief valve 104 to the external environment 102 (i.e. outside the larger building 110). In the illustrated embodiment, the vent pipe vents through the roof of the building (See FIGS. 1 and 3).
A typical section of pipework containing a conventional pressure relief valve is shown in FIG. 2. In the illustrated application, the relief valve 104 includes a pressure valve arrangement that opens in response to excessive positive pressure within the controlled atmosphere room. When the pressure valve is open, air is free to vent to the external environment, thereby reducing internal pressure. The illustrated relief valve also includes a vacuum valve arrangement that opens in response to excessive negative pressure within the controlled atmosphere room. When the negative valve is open, air is drawn from the overhead space 114 into the controlled atmosphere room to adequately equalize pressure. In the illustrated application, the pressure relief valve 104 is connected in parallel with a water-filled trap pressure bypass 116 that functions as a back-up system to allow pressure equalization even if the relief valve fails. As show in FIG. 2, the pressure bypass 116 may include a water trap 118 that contains an amount of water selected to set the desired bypass pressure. When a positive or negative pressure differential becomes great enough, air can bubble through the water trap 118. A typical trap pressure bypass arrangement not only requires additional pipework, but also requires ongoing maintenance. For example, the appropriate amount of water must be maintained within the trap 118. This may require a serviceman to periodically check the status of the water column and add water (or other fluids) as evaporation affects the system.
In a conventional system, the pipework required to implement the pressure/vacuum relief system is extensive, resulting in significant installation cost and occupying a substantial amount of space within the building. These issues are compounded in buildings that include a plurality of controlled atmosphere rooms 100. For example, FIG. 4 shows the crowded overhead space 114 of the building 110 of FIGS. 1 and 3. This illustration shows the relief system pipework for the six controlled atmosphere rooms 100, as well as additional pipework for other facilities/services associated with the controlled atmosphere rooms.